Question about Christoffel symbol's value

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    Christoffel Value
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The discussion centers on the formal proof that the Christoffel symbols can be made to vanish locally at a point using normal coordinates. By applying the rectification theorem, the geodesics passing through a point can be transformed into straight lines, demonstrating that under this diffeomorphism, the Christoffel symbols indeed vanish. The proof involves showing that the exponential map from the tangent space T_pM to the manifold M is a local diffeomorphism, followed by defining local coordinates using an orthonormal basis of T_pM. This process confirms that in normal coordinates, the geodesic equations simplify, resulting in zero Christoffel symbols.

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raopeng
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In my geometry textbook it is stated that intuitively we can choose a suitable basis of coordinates that the components Christoffel symbol vanishes locally at that point(= 0). However can one obtain a formal proof of it? For example if we use rectification theorem to rectify the geodesics passing through a point into straight lines, can we say under such diffeomorphism the Christoffel symbol vanishes since the geodesic is mapped into a line in the neighbourhood of that point?
 
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Formally, this is the existence of normal coordinates. See for instance Lee (Riemannian manifolds, p.76-78)

First you prove that the exponential map T_pM-->M v-->"geodesic through p with initial speed v evaluated at t=1" is a local diffeomorphism using the inverse function theorem. Then you pick a g_p-orthonormal basis of T_pM and use this together with the exponential map to define local coordinates of M around p (normal coordinates). In these coordinates, geodesics are straight lines. Then stare at the geodesic equation in these coordinates. Clearly, the Christofel symbols all vanish.
 
Thank you, it puts everything in its place
 

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